Antibacterial mechanism of ultrasound against Escherichia coli: Alterations in membrane microstructures and properties

• Published in: Ultrasonics sonochemistry Vol. 73; p. 105509
• Main Authors: He, Qiao, Liu, Donghong, Ashokkumar, Muthupandian, Ye, Xingqian, Jin, Tony Z., Guo, Mingming
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01-05-2021; Elsevier
• Subjects: Antimicrobial mechanism; Escherichia coli O157:H7; Membrane permeability; Original; Ultrasonic field; Ultrasonic field; Antimicrobial mechanism; Escherichia coli O157:H7; Membrane permeability
• ISSN: 1350-4177; 1873-2828
• DOI: 10.1016/j.ultsonch.2021.105509

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•The antibacterial effect of US was in a time- and intensity-dependent manner.•US remarkably increased the sensitivity of E. coli cells to TEON.•US significantly increased the outer and inner membrane permeability.•US resulted in membrane fluidity reduction and membrane depolarization.•US caused conformational and compositional changes in some membrane components.
This study was aimed at providing new insights on the response of bacterial cell membranes to ultrasound exposure. Escherichia coli (E. coli) O157:H7 cells were exposed to different ultrasound treatments (power intensities of 64, 191, 372, and 573 W/cm2, frequency of 20 kHz, pulsed mode of 2 sec: 2 sec) and the dynamic changes in cell viability within 27 min were assessed. With an increase in ultrasonic intensity and prolonged duration, a 0.76–3.52 log CFU/mL reduction in E. coli populations was attained. The alterations in the sensitivity of ultrasound-treated cells to antimicrobial compounds were evaluated by exposure to thyme essential oil nanoemulsion (TEON). The treatment reduced the E. coli population by 2.16–7.10 log CFU/mL, indicating the effects of ultrasonic field on facilitating the antibacterial efficacy of TEON. Ultrasonic-treated E. coli cells also displayed remarkable morphological and ultrastructural damages with destroyed membrane integrity and misshaped cell structures, which was observed by electron microscopy analysis. Significant increase in outer and inner membrane permeability, along with the cytoplasmic leakage and membrane depolarization were assessed utilizing spectrophotometry. For the first time, significant reduction in the membrane fluidity in response to ultrasound exposure were investigated. Additional efforts in exploring the effect of ultrasonic field on some bacterial membrane compositions were performed with infrared spectroscopy. In this study, multiple lines of evidence effectively served to elucidate the alterations on cellular membrane structure and property during exposure to sonication that could extend our understanding of the antimicrobial molecular mechanisms of ultrasound.